The Blue Block engines werent anything more than what was found in any other GM vehicle of the time, most Blue Blocks were produced from 77 to 79.
A Blue Block 4 bolt main engine compared to any other 4 bolt main small block engine is no different.
Later versions had the oil dipstick relocated to the passengers side of the engine, but this was done to all small block GM engines.
The color of the block normally denoted that the engine came from a Camero or Corvette, but true heritage needs to be determined by the casting numbers, even then it doesnt mean the engine is worth any more due to the fact that 4 bolt main engines can be found in everything from trucks, Impala's, Nova's, Malibu's, and Station wagons, GM used the 4 bolt main engines as a "Heavy Duty" engine and at times it could be found in any vehicle they produced that could be purchased with a small block V-8.
So to answer your question his Blue Block engine is worth the same as any other 4 bolt main 350, the only way the value might go up is if you could find the original vehicle it came from along with the transmission and it was restoreable and you had someone willing to pay the extra for numbers matching.

Yea BUick used blue for their standard engine color.
The blue blocks this refers to were always thought to be some type of hypo engine but the reality is they were basic assembly line engines painted a different color to take advantage of sales strategy.

Thanks for the edumacation TB , it is appreciated. I like these posts where we bring back some of the uniqueness of gm.

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This little tidbit of knowledge cost me a couple hundred dollars back in the day, I didnt know a thing about Blue Blocks except that all the drag racers wanted them (for the 4 bolt mains), so thinking they were special factory hotrod engines I fell for it hook line and sinker and bought one from a guy that barely new more than me (except he knew how to get more of my money than he should have), when I brought the engine to a machine shop owned by a friend of my fathers to get machine work done he schooled me on the heritage of the "Blue Block".
My fathers friend was a GM engineer that left GM during the early 70's to work for GM's Winston Cup engine development program back when all the manufacturers were chased out of racing sponsorship, so I figured he should know a thing or two about GM engines.